Method of forming all skin viscose rayon



Unite States Patent Chine 2,895,788 Patented July 21, 1959 METHOD OFFORMING ALL SKIN VISCOSE RAYON John A. Howsmon, Wilmington, Del'., andByron A. Thumm, Prospect Park, Pa., assignors to American ViscjoseCorporation, Philadelphia, Pa.-, a corporation of Delaware N 0 Drawing.ApplicationDec'ember S0, 1954 Serial N0. 478,914

8 Claims. (Cl. 18-54) This invention relates to the production of shapedbodies of regenerated cellulose from viscose and more particularly tofilaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regeneratedcellulose from. viscose, a suitable cellulosic material such as purifiedcotton linters, wood pulp, mixtures thereof, and the like is firstconverted to an alkali cellulose by treatment with a caustic sodasolution and after shredding the treated cellulose material, it isallowed to age. The aged alkali cellulose is then converted to axanthate by treatment with carbon disulifide. The cellulose xanthate issubsequently dissolved in a caustic sodasolution in an amount calculatedto provide a" viscose of the desired cellulose and alkali content.-After filtration, the viscose solution is allowed to ripen andissubsequently extruded through a shaped orifice into a suitablecoagulating and regenerating bath.

In: the production of shaped bodies such as filaments, the viscosesolution is extruded through a spinneret into a coagulating andregenerating bath consisting of an aqueous acid solution containing zincsulfate. The filament may subsequently be passed through ahot aqueousbath where it is stretched to improve its properties such as tensilestrength. The filament may then be passed through a dilute aqueoussolution of sulfuric acid and sodium sulfate to-complete theregeneration of the cellulose,- in case it is not completelyregeneratedupon leaving the stretching, stage. The filament issubsequently subjected to washing, purification, bleaching, possiblyother treating operations and drying, being collected either before orafter these treatments.-

The filaments as formed by the conventional methods consist of a skinor. outer shell portion and acore portion with a sharp line ofdemarkation between the two. The cross-section of the filaments exhibitsavery irregular or crenulated exterior surface when even small amountsof zinc salts or certain other polyvalent metal salts are pres ent inthe spinning bath. The skin and core portions of the filament representdifferences in structure and these different portions possess differentswelling and staining characteristics, the latter permitting a readyidentification of skinand core. The sharply irregular and crenulatedsurface structure has a relatively low abrasion resistance and readilypicks up foreign particles such asdirt. Although the core portionpossesses a relatively high tensile strength, it has a low abrasionresistance and a low flexlife, is subject to fibrillation and isrelatively stifi.

It has now. been discovered that the presence of small amounts ofcholine .and certain water-soluble choline salts in viscose results inthe production of shaped bodies of regenerated cellulose such asfilaments, films, sheets and the like composed of all skin and havingimproved properties and characteristics providing that the amount of thecholine or choline salt is maintained with certain limits andthecomposition of the spinning bath is maintained within certaincomposition limits which will be defined hereinafter; The most readilydistinguishable 2v characteristics as compared to conventional filamentsinclude asmo'ot'h, non-crenulated surface and the filaments consistentirely of skin.

Choline salts which are satisfactory for the purposes of this inventioninclude both inorganic and organic anions such as the halides, forexample, the chloride and the bromide, sulfates, for example, thesulfate and the bisulfate, the acetate, the propionate, etc. Mixtures ofcholine with one or more salts and mixtures of the salts are alsosatisfactory. The modifier may be conveniently added in the form of asolution in water or in a caustic soda solution.

The amount of the choline or choline salt which is incorporated in theviscose must be at least about 0.3% by weight of the cellulose in theviscose and may vary to about 4.5%, preferably, the amount varies from0.5% to 2.5%. Lesser amounts do not result in the production of productsconsisting entirely of skin and greater amounts affect adversely thephysical properties of the products. Amounts within the preferred rangeare mosteifective in enhancing the characteristics and properties of theproducts. The choline or choline salt may he added at any desired stagein the production of the viscose such as in the preparation of therefined wood pulp for the manufacture of viscose, before or during theshredding of the alkali cellulose, to the xanthated cellulose whileit isbeing dissolved in the caustic solution or to the viscose solutionbefore or after filtration. The choline or choline salt is preferablyadded after the cellu' lose xanthate has been dissolved in the causticsolution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, theparticular source of the cellulose being selected for the ultimate useof the regenerated cellulose product. The caustic soda content may befrom about 4% to about 8% and the carbon disulfide contentmay be fromabout 30% to about 50% based upon the weight of the cellulose. Themodified viscose, that is, a viscose containing the small amount ofcholine or a choline salt, may have a salt test above about 7 andpreferably above about 9 at the time of spinning or extrusion. The termsalttest as used herein refers to the conventional sodium chloride salttest.

Inorder to obtain the improvements enumerated hereinbefore, it isessential that the composition of the spin: ning bath bemaintainedwithina well-defined range. The presence of the choline or choline salt in theviscose combined with these limited spinning baths results in theproduction. of yarns of improved properties such as high tenacity, highabrasion-resistance, high fatigue resistance and consisting of filamentscomposed entirely of skin.

Generically and in terms of the industrial. art, the spinning bath is alow acid-high zinc spinning bath containing from about 10% to about 25%sodium sulfate and from about 3% to about 15% zinc sulfate, preferablyfrom 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Othermetal sulfates such as iron, manganese, nickel and the like may bepresent and may replace some of the zinc sulfate. The temperature of thespinning bath may vary from about 25 C. to about 80" C., preferablybetween about 45 C. and about C. In the production of the all skin typefilaments, the temperature of the spinning bath is not critical,however, as is well known in the conventional practice in the art,certain of the physical properties such as tensile strength varydirectly with the temperature of thespinning bath. Thus, in theproduction of filaments for tire cord purposes in accordance with themethod of this invention, the spinning bath is preferably maintained ata temperature between .about 55 C. and 65 C. so as to obtain the desiredhigh tensile strength.

The acid content of the spinning bath is balanced against'thecomposition of the viscose. The lower limit of the acid concentration,as is well known in the art, is just above the slubbing point, that is,the concentration at which small slubs of uncoagulated viscose appear inthe strand as it leaves the spinning bath. For commercial operations,the acid concentration of the spinning bath is generally maintainedabout 0.4% to 0.5% above the slubbing point. For any specific viscosecomposition, the acid concentration of the spinning bath must bemaintained above the slubbing point and below the point at which theneutralization of the caustic of the viscose is sufficiently rapid toform a filament having a skin and core.

There is a maximum acid concentration for any specific viscosecomposition beyond which the neutralization is sufiiciently rapid toproduce filaments having a skin and core. For example, in general, theacid concentration of the spinning baths which are satisfactory for theproduction of the all skin products from a 7% cellulose, 6%caustic-viscose and containing choline or a choline salt lies betweenabout and about 8%. The acid concentration may be increased as theamount of the modifier is increased and also as the salt test of theviscose is increased. There is an upper limit, however, for the acidconcentration based upon the amount of modifier and the concentration ofcaustic in the viseose. All skin products cannot be obtained if the acidconcentration is increased above the maximum value although the amountof the choline or choline salt is increased beyond about 4.5% whileother conditions are maintained constant. Increasing the caustic sodacontent of the viscose beyond about 8% is uneconomical for commercialproduction methods. For example, a viscose containing about 7%cellulose, about 6% caustic soda, about 41% (based on the weight ofcellulose) carbon disulfide, and 1% (based on the weight of cellulose)of choline or a choline salt and having a salt test of about whenextruded into spinning baths containing 16 to 20% sodium sulfate, 4 to8% zinc sulfate and sulfuric acid not more than about 7.8% results inthe production of all skin filaments. Lesser amounts of sulfuric acidmay 'be employed. Greater amounts of sulfuric acid result in theproduction of products having skin and core. A lowering of the amount ofthe modifier, the lowering of the caustic soda content or the loweringof the salt test of the viscose reduces the maximum permissible acidconcentration for the production of all skin filaments. It hasbeendetermined that the maximum concentration of acid which is permissiblefor the production of all skin products is about 8.5%.

The presence of the choline or choline salt in the viscose retards thecoagulation and, therefore, the amount of derivative employed must bereduced at high spinning speeds. Thus, for optimum physicalcharacteristics of an all skin yarn formed from a viscose as above andat a spinning speed of about 50 meters per minute, the modifier isemployed in amounts within the erating bath preferably between 85% and100%. Yarns for other textile purposes may be stretched as low as 20%.The precise amount of stretching will be dependent upon the desiredtenacity and other properties and the specific type of product beingproduced. It is to be understood that the invention is not restricted tothe production of filaments and yarns but it is also applicable to othershaped bodies such as sheets, films, tubes and the like. The filamentsmay then be passed through a final regenwhich may contain from about 1%to about 5% sulfuric acid and from about 1% to about 5% sodium sulfatewith or without small amounts of zinc sulfate if regeneration has notpreviously been completed. The treatment following the finalregenerating bath, or the stretching operation where regeneration hasbeen completed may consist of a washing step, a desulfurizing step, theapplication of a finishing or plasticizing material and drying before orafter collecting, or may include other desired and conventional stepssuch as bleaching and the like. The treatment after regeneration will bedictated by the specific type of shaped body and the proposed usethereof. Regenerated cellulse filaments prepared from viscose containingthe small amounts of choline or choline salts and spun in the spinningbaths of limited acid content have a smooth or non-crenulated surfaceand consist entirely of skin. Because of the uniformity of structurethroughout the filament, the swelling and staining characteristics areuniform throughout the cross-section of the filament. Filaments producedpursuant to this invention and consisting entirely of skin have a hightoughness and a greater flexing life than filaments as producedaccording to prior methods which may be attributed by the uniformity inskin structure throughout the filament. Although the twisting ofconventional filaments, as in the production of tire cord, results in anappreciable loss of tensile strength, there is appreciably less loss intensile strength in the production of twisted cords from the l filamentsconsisting entirely of skin. Filaments prepared the weight of thecellulose.

lower portion of the range, for example, about 1% The determination ofthe specific maximum and optimum concentration of acid for any specificviscose, spinning bath and spinning speed is a matter of simpleexperimentation for those skilled in the art. The extruded viscose must,of course, be immersed or maintained in the spinning bath for a periodsufiicient to effect relatively complete coagulation of the viscose,that is, the coagulation must be sufiicient so that the filaments willnot adhere to each other as they are brought together and withdrawn fromthe bath.

In the production of filaments for such purposes as the fabrication oftire cord, the filaments are preferably stretched after removal from theinitial coagulating and regenerating bath. From the initial spinningbath, the filaments may be passed through a hot aqueous bath which mayconsist of hot water or a dilute acid solution and may be stretched fromabout 70% to about 120%,

from viscose containing choline or choline salts have a high tensilestrength as compared to normal regenerated cellulose filaments, havesuperior abrasion and fatigue resistance characteristics and have a highflexlife. Such filaments are highly satisfactory for the production ofcords for the reinforcement of rubber products such as pneumatic tirecasings, but the filaments are not restricted to such uses and may beused for other textile applications.

The invention may be illustrated by reference to the preparation ofregenerated cellulose filaments from a viscose modified with cholinechloride and containing about 7% cellulose, about 6% caustic soda, andhaving a total carbon disulfide content of about 41% based on The vicosesolutions were prepared by xanthating alkali cellulose by theintroduction of 36% carbon disulfide based on the weight of thecellulose and churning for about 2 /2 hours. The cellulose xanthate wasthen dissolved in caustic soda solution. An additional 5% carbondisulfide was then added to the mixer and the mass mixed for about onehour. The desired amount of modifier was added to the solution and mixedfor about /2 hour. The viscose was then allowed to ripen for about 30hours at 18 C.

Example 1 Approximately 0.7% (based on the weight of the cellulose)choline chloride was added to and incorporated in the viscose asdescribed above. The viscose employed in the spinning of filaments had asalt test of 11. The viscose .was extruded through a spinneret to form a200 denier, 120 filament yarn at a rate of about 22 meters per minute.The coagulating and regenerating bath was maintained at a temperature ofabout 60 C.

and contained 7.7% sulfuric acid, 8.3% zinc sulfate and 18% sodiumsulfate. The yarn was stretched about 82% 4 while passing, through a hotwater bath at 95" C1 The yam was collected in a spinning box, washedfree of acids and salts and dried.

The individual filaments have a. smooth, non-crenufated exterior surfaceand consist entirely of skin, no core beingdetectable at highmagnification (e.-g. 1500X). The. filaments of a control. yarn. spunwith the. same. viscose but: without the addition. of the. modifiedagent and spun-under the. same conditions, exhibit a very irregular and.serrated surface and are composed of about 75 skin. and the balance corewith. a sharp line of demarkation between the skin and core. Otherphysical propertiesv are set forth in the table which follows theexamples.

Example 2 To a viscose as described above, there was added 1.4% (basedon the weight off the cellulose) choline chloride. The viscose had asalt test of 10.8 and was spun into a 200 denier, 120 filament yarn byextrusion into a spinning bath containing 7.8%. sulfuric acid, 8.3%zinc. sulfate and 18% sodium sulfate; The bath was maintained at 61 C.and the extrusion rate was about 22. meters per minute. The filamentswere subsequently passed through a hot water bath at 95 C. and stretchedabout 82%. The yarn was collected in a spinning box, washed free ofacids and salts and dried.

The individual filaments were readily distinguishable from controlfilaments in that they have a smooth, noncrenulated surface. and consistentirely of skin while the control filaments have a very irregular andserrated surface and consist of about 75 skin and the balance core witha sharp line of demarkation between the skin and core. Other phyicalproperties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 1%(based on the weight of the cellulose) choline chloride. The viscose hada salt test of 10 and was spun into a 1650 denier, 720 filament cord byextrusion into a bath containing 7.2% sulfuric acid, 8% zinc sulfate and17% sodium sulfate. The bath was maintained at a temperature of 60 C.The extrusion rate was about 21 meters per minute. The water bath wasmaintained at about 95 C. and the filaments were stretched approximately90% while passing through the hot water. The cord was washed free ofacid and salts by treatment with water at about 95 C. onthread-advancing reels, and dried and collected on cones.

The individual filaments were readily distinguishable from controlfilaments prepared from viscose containing no modifier in that they havea smooth, non-crenulated surface and consist entirely of skin. Controlfilaments have a very irregular and serrated surface and consist ofabout 75% skin and the balance core with a sharp line of demarkationbetween the skin and core. Other physical properties are set forth inthe table which follows "the examples.

Example 4 As a control for the foregoing examples, a viscose solution,prepared as described above, having a salt test of 10 was spun into a210 denier, 120 filament yarn by extrusion into a bath containing 7.6%sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath wasmaintained at a temperature of about 60 C. The extrusion rate was about22 meters per minute. The water bath was maintained at a temperature ofabout 95 C. and the filaments were stretched 82% while passing throughthe hot water. The yarn was collected in a spinning box, Washed free ofacid and salts and dried.

The individual filaments have a very irregular and serrated surface andconsist of about 75 skin and the balance core with a sharp line ofdemarkation between the skin and the core. Other. characteristics are;set forth in the table which follows:

Although the tenacity and elongation are the only properties set forth,they have been chosenv because of the ease and simplicity with whichsuch properties may be determined. In some instances, products. made inaccordance with this invention do not exhibit large or greatimprovements in. tenacity and elongation, however, the products consistof a smooth-surfaced, all skinv structure and possess improved abrasion.resistance, flex-life and other properties. as. disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is itsrelatively high cross-sectional swelling when wet with water, thisswelling amounting to from about 65% to about for rayon produced byconventional methods. Rayon filaments produced in accordance with themethod of this invention have an appreciably lower crosswsectionalswelling Characteristic, the swelling amounting to from about 45% toabout 60%.

The choline or choline salt may be added to any desired viscose such asthose normally used in industry, the specific viscose composition setforth above, being merely for illustrative purposes. The modifying agentmay be added at any desired stage in the production of the viscose andmay be present in the cellulosic raw material although it may benecessary to adjust the amount present .to produce a viscose having theproper proportions of the adduct at the time of spinning.

If desired, small amounts of the modifying agent may be added to thespinning bath. Since the choline and choline salts are water-soluble,some of the modifier will be leached from the filaments and will bepresent in the bath.

The term skin is employed to designate that portion of regeneratedcellulose filaments which is permanently stained or dyed by thefollowing procedure: A microtome section of one or more of the filamentsmounted in a wax block is taken and mounted on a slide with Meyersalbumin fixative. After dewaxing in xylene, the section is placed insuccessive baths of 60% and 30% alcohol for a few moments each, and itis then stained. in 2% aqueous solution of Victoria Blue BS conc. (Gen--eral Dyestuffs Corp.) for 1 to 2 hours. At this point,. the entiresection is blue. By rinsing the section first in. distilled water andthen in one or more baths composed of 10% water and dioxane for a periodvarying; from 5 to 30 minutes depending on the particular filament, thedye is entirely removed from the core, leaving it restricted to the skinareas.

While preferred embodiments of the invention have been disclosed, thedescription is intended to be illustra-- tive and it is to be understoodthat changes and variations may be made without departing from thespirit and scope of the invention as defined by the appended claims.

We claim:

1. In a method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin, the step which comprisesextruding viscose containing from about 0.3% to about 4.5%, based on theweight of the cellulose, of a modifying agent selected from the: groupconsisting of choline, choline chloride, choline bromide, cholinesulfate, choline bisulfate, choline acetate and choline propionate andmixtures thereof into an aqueous spinning bath containing from about to25% sodium sulfate, from about 3% to zinc sulfate and sulfuric acid, thesulfuric acid content 'of the spinning bath exceeding the'slubbing pointbut not exceeding about 8.5%.

2. The step in the method as defined in claim 1 wherein the modifyingagent comprises choline.

3. The step in the method as defined in claim 1 wherein the modifyingagent comprises choline chloride.

4. In a method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin, the steps which compriseadding to and incorporating in viscose from about 0.3% to about 4.5%,based on the weight of the cellulose, of a modifying agent selected fromthe group consisting of choline, choline chloride, choline bromide,choline sulfate, choline bisulfate, choline acetate and cholinepropionate and mixtures thereof, and extruding the viscose into anaqueous spinning bath containing from about 10% to 25% sodium sulfate,from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acidcontent of the spinning bath exceeding the slubbing point but notexceeding about 8.5%.

5. The method as defined in claim 4 wherein the modifying agentcomprises choline.

' 6. The method as defined in claim 4 wherein the modifying agentcomprises choline chloride.

7. In a method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin, the steps which compriseadding to and incorporating in viscose from about 0.5% to about 2.5%,based on the -8 weight. .of the cellulose, of a modifying agent selectedfrom the group consisting of choline, choline chloride, choline bromide,choline sulfate, choline bisulfate, choline acetate and cholinepropionate' and mixtures thereof, the viscose containing about 7%cellulose, about 6% caustic soda and about 41%. carbon disulfide basedupon the weight ofthe cellulose, ripening the viscose to a sodiumchloride salt point of not lower than 9 and extruding the viscose intoan aqueous spinning bath containing from about 16% to 20% sodiumsulfate, from about 4% to 9% zinc sulfate and sulfuric acid, thesulfuric acid content of the spinning bath exceeding the slubbing pointbut not exceeding about 8.5

8. The method as defined in claim 7 wherein the modifying agentcomprises choline chloride.

References Cited in the file of this patent UNITED STATES PATENTS2,125,031 Polak July 26, 1938 2,312,152 Davis Feb. 23, 1943 2,335,980Waltman Dec. 7, 1943 2,373,712 Schlosser Apr. 17, 1945 2,593,466MacLaurin Apr. 22, 1952 2,648,611 Richter Aug. 11, 1953 2,705,184 DrischMar. 29, 1955 2,732,279 Tachikawa Jan. 24, 1956 FOREIGN PATENTS 736,107France Nov. 19, 1932 379,260 Great Britain Aug. 25, 1932

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING FROM ABOUT 0.3% TO ABOUT 4.5% BASED ON THE WEIGHT OF THE CELLULOSE, OF A MODIFYING AGENT SELECTED FROM THE GROUP CONSISTING OF CHOLINE CHOLINE CHLORIDE, CHOLINE BROMIDE, CHOLINE SULFATE, CHOLINE BISULFATE, CHOLINE ACETATE AND CHOLINE PROPIONATE AND MIXTURES THEREOF INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 8.5% 